Boron Halides Lewis Acidity Simulator

Lewis Acid Strength of Boron Halides

Visualizing the impact of orbital size mismatch on pπ-pπ back bonding.

1. Select Molecule

BF₃

BCl₃

BBr₃

BI₃

Lewis Acid Strength Weak

2. Visualization Controls

Boron 2p Orbital (Empty) Halogen p Orbitals (Filled) π-Backbonding Density Auto-Rotate

3. Chemical Principles

The Anomaly: Based solely on electronegativity, one might expect BF₃ to be the strongest Lewis acid because Fluorine is the most electronegative. However, experimentally, BF₃ is the weakest, and BI₃ is the strongest.

The Explanation (Orbital Overlap):
Boron's empty orbital is a small 2p orbital. For back bonding to be effective, the halogen's filled p-orbital must be of a similar size.

• F (2p): Perfect size match. Excellent 2pπ-2pπ overlap. Boron's electron deficiency is heavily compensated.
• I (5p): Massive size mismatch. Terrible 2pπ-5pπ overlap. Back bonding is negligible, leaving Boron highly electron deficient (Strong Acid).

Orbital Overlap

2pπ - 2pπ

Left Click + Drag to Rotate • Scroll to Zoom

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